Meteoric fluid‐rock interaction in Variscan shear zones     

Camille Dussaux  Aude Gbelin  Philippe Boulvais  Vronique Gardien  Stephen Grimes  Andreas Mulch 《地学学报》2019,31(4):366-372

Variscan shear zones in the Armorican Massif represent sites of strong fluid‐rock interaction. The hydrogen isotope composition of muscovite (δD_Ms) from syntectonic leucogranite allows to determine the source of fluids that infiltrated the footwall of three detachment zones and the South Armorican Shear Zone. Using temperatures of hydrogen isotope exchange estimated from microstructural data, we calculate the hydrogen isotope ratios of water (δD_water) present within the shear zones during high‐temperature deformation. A ~40‰ difference in δD_water values from deep to shallow crustal level reveals a mixing relationship between deep crustal fluids with higher δD values that range from ?34 to ?33‰, and meteoric fluids with δD values as low as ?74‰ in the upper part of detachment footwalls.  相似文献   

Evaluation of NLDAS‐2 evapotranspiration against tower flux site observations          下载免费PDF全文

Youlong Xia  Michael T. Hobbins  Qiaozhen Mu  Michael B. Ek 《水文研究》2015,29(7):1757-1771

The North American Land Data Assimilation System project phase 2 (NLDAS‐2) has run four land surface models for a 30‐year (1979–2008) retrospective period. Land surface evapotranspiration (ET) is one of the most important model outputs from NLDAS‐2 for investigating land–atmosphere interaction or to monitor agricultural drought. Here, we evaluate hourly ET using in situ observations over the Southern Great Plains (Atmospheric Radiation Measurement/Cloud and Radiation Testbed network) for 1 January 1997–30 September 1999 and daily ET u‐sing in situ observations at the AmeriFlux network over the conterminous USA for an 8‐year period (2000–2007). The NLDAS‐2 models compare well against observations, with the National Centers for Environmental Prediction's Noah land surface model performing best, followed, in order, by the Variable Infiltration Capacity, Sacramento Soil Moisture Accounting, and Mosaic models. Daily evaluation across the AmeriFlux network shows that for all models, performance depends on season and vegetation type; they do better in spring and fall than in winter or summer and better for deciduous broadleaf forest and grasslands than for croplands or evergreen needleleaf forest. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Erratum to: Drivers and mechanisms for enhanced summer monsoon precipitation over East Asia during the mid-Pliocene in the IPSL-CM5A     

Yong Sun  Tianjun Zhou  Gilles Ramstein  Camille Contoux  Zhongshi Zhang 《Climate Dynamics》2016,46(5-6):2027-2027

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印度尼西亚北苏拉威西红树林生态系统碳库研究     

陈顺洋  陈彬  SASTROSUWONDO Pramudji  DHARMAWAN I Wayan Ek  欧丹云  尹希杰  俞炜炜  陈光程 《海洋学报(英文版)》2018,37(12):85-91

近年来的研究指出红树林在海岸带碳固定和碳储存方面发挥着重要的作用。尽管印度尼西亚的红树林面积在全球占很大的比重,对于该地区红树林的有机碳储量和土壤有机碳来源的认识仍有限。本研究调查了印度尼西亚北苏拉威西海洋型的Wori红树林中生态系统有机碳储量及其空间分布特征,以及土壤有机碳的来源,以期加深该地区红树林“蓝碳”功能的认识。研究结果显示,Wori红树林0-50cm深度土壤中有机碳储量为15.4 kg/m²,占生态系统碳储量的主要部分（65%）。红树植物生物量和生态系统碳储量分别为8.3 kg/m²和23.7 kg/m²。土壤有机碳储量在不同离岸距离的采样站位中未表现出显著的空间分布差异,而生物量碳储量则在外滩最高。¹³C稳定同位素分析结果表明红树林土壤中蓄积的有机碳主要来源于红树林有机质,而潮水中的悬浮有机质和红树林外缘的海草并不构成红树林土壤有机碳的重要来源,它们的贡献者都低于20%。研究结果进一步证实了热带地区海洋型红树林湿地在碳储存以及红树植物对碳固定方面的重要性。  相似文献   

Sedimentary archives of the French Atlantic coast (inner Bay of Vilaine,south Brittany): Depositional history and late Holocene climatic and environmental signals     

Philippe Sorrel  Bernadette Tessier  François Demory  Agnès Baltzer  Firas Bouaouina  Jean-Noël Proust  David Menier  Camille Traini 《Continental Shelf Research》2010,30(10-11):1250-1266

The late Holocene is of particular interest to our understanding of the evolution of coastal sedimentary systems because this period encompasses warmer and cooler periods, and rising sea level in northern Europe. Based on an approach combining AMS ¹⁴C, sedimentological and rock magnetic analyses on sediment cores complemented with seismic data collected in the macrotidal Bay of Vilaine (south Brittany), we document the depositional history of the inner bay coeval to the mid- to late-Holocene transgression in south Brittany. Correlation between sedimentary archives revealed the main sedimentary infilling phases during the last 6000 years. Four units (U1–U4) are recognized in the coastal sediment wedge of the system, corresponding to the stepwise marine invasion of the bay. We show that (1) marine inundation, due to the steep morphology of the bedrock, is diachronous between distal and proximal records. A time lag of ～1000 years is inferred over a distance of less than 5 km; (2) in the outer areas, the sedimentation has been condensed since 3000 years; (3) proximal estuarine archives offer the best record of sedimentary processes covering the last 2000 years, including the Medieval Warm Period (MWP).Correlations in proximal records in the Bay of Vilaine assess the connection between coastal sedimentary dynamics, climatic conditions and anthropogenic activities during the MWP. We match the preservation of clay deposits to increased river-borne suspended matter transported to the estuary probably as a result of accelerated land-use development (higher soil erosion) in the catchment area between ca. 880 and 1050 AD. Because the preservation of estuarine sedimentary successions is favoured when coastal wave sediment reworking is minimal, it is proposed that the prevailing climatic regime in south Brittany during the MWP likely resembled to that of the preferred negative phase of the North Atlantic Oscillation (NAO). Our data are fairly consistent with other late Holocene records from northern Europe including the Atlantic seaboard. However, they outline the difficulty in interpreting climatic and anthropogenic signatures in coastal sedimentary records where high-resolution chronologies required to unravel their respective influences are still missing.  相似文献   

Single-Column Model Intercomparison for a Stably Stratified Atmospheric Boundary Layer   总被引：2，自引：15，他引：2  

J. Cuxart  A. A. M. Holtslag  R. J. Beare  E. Bazile  A. Beljaars  A. Cheng  L. Conangla  M. Ek  F. Freedman  R. Hamdi  A. Kerstein  H. Kitagawa  G. Lenderink  D. Lewellen  J. Mailhot  T. Mauritsen  V. Perov  G. Schayes  G-J. Steeneveld  G. Svensson  P. Taylor  W. Weng  S. Wunsch  K-M. Xu 《Boundary-Layer Meteorology》2006,118(2):273-303

The parameterization of the stably stratified atmospheric boundary layer is a difficult issue, having a significant impact on medium-range weather forecasts and climate integrations. To pursue this further, a moderately stratified Arctic case is simulated by nineteen single-column turbulence schemes. Statistics from a large-eddy simulation intercomparison made for the same case by eleven different models are used as a guiding reference. The single-column parameterizations include research and operational schemes from major forecast and climate research centres. Results from first-order schemes, a large number of turbulence kinetic energy closures, and other models were used. There is a large spread in the results; in general, the operational schemes mix over a deeper layer than the research schemes, and the turbulence kinetic energy and other higher-order closures give results closer to the statistics obtained from the large-eddy simulations. The sensitivities of the schemes to the parameters of their turbulence closures are partially explored.  相似文献   

Pelagic tar off Georgia and Florida in relation to physical processes     

Camille Cordes  Larry Atkinson  Richard Lee  Jack Blanton 《Marine pollution bulletin》1980,11(11):315-317

Following the Ixtoc I oil rig blowout in Campeche Bay we hypothesized that resulting tarballs should eventually appear in the Gulf Stream off Gerogia and that because of dynamic barriers in the innershelf little would reach nearshore areas. To test these hypotheses, surface tows to collect floating tar were taken off the coasts of Georgia and Florida in October and December, 1979.No tar was found within 40 km of the shore. All samples more than 40 km offshore contained some tar. The mean concentration was 0.82 mg m^?2 with a range of 0.01–5.6 mg m^?2. Closely spaced sampling showed extreme variation but trends were consistent. Perylene was the most abundant compound in the tarballs.  相似文献   

Speciation of naturally-accumulated uranium in an organic-rich soil of an alpine region (Switzerland)     

Simona Regenspurg  Camille Margot-Roquier  Pascal Froidevaux  Pilar Junier 《Geochimica et cosmochimica acta》2010,74(7):2082-2098

Very high concentrations of uranium (up to 4000 ppm) were found in a natural soil in the Dischma valley, an alpine region in the Grisons canton in Switzerland. The goal of this study was to examine the redox state and the nature of uranium binding in the soil matrix in order to understand the accumulation mechanism. Pore water profiles collected from Dischma soil revealed the establishment of anoxic conditions with increasing soil depth. A combination of chemical extraction methods and spectroscopy was applied to characterize the redox state and binding environment of uranium in the soil. Bicarbonate extraction under anoxic conditions released most of the uranium indicating that uranium occurs predominantly in the hexavalent form. Surprisingly, the uranium redox state did not vary greatly as a function of depth. X-ray absorption near edge spectroscopy (XANES), confirmed that uranium was present as a mixture of U(VI) and U(IV) with U(VI) dominating. Sequential extractions of soil samples showed that the dissolution of solid organic matter resulted in the simultaneous release of the majority of the soil uranium content (>95%). Extended X-ray absorption fine structure (EXAFS) spectroscopy also revealed that soil-associated uranium in the soil matrix was mainly octahedrally coordinated, with an average of 1.7 axial (at about 1.76 Å) and 4.6 to 5.3 equatorial oxygen atoms (at about 2.36 Å) indicating the dominance of a uranyl-like (UO₂²⁺) structure presumably mixed with some U(IV). An additional EXAFS signal (at about 3.2 Å) identified in some spectra suggested that uranium was also bound (via an oxygen atom) to a light element such as carbon, phosphorus or silicon. Gamma spectrometric measurements of soil profiles failed to identify uranium long-life daughter products in the soil which is an indication that uranium originates elsewhere and was transported to its current location by water. Finally, it was found that the release of uranium from the soil was significantly promoted at very low pH values (pH 2) and increased with increasing pH values (between pH 5 and 9).  相似文献   

Sediment Accretion in Tidal Freshwater Forests and Oligohaline Marshes of the Waccamaw and Savannah Rivers,USA     

Scott H. Ensign  Cliff R. Hupp  Gregory B. Noe  Ken W. Krauss  Camille L. Stagg 《Estuaries and Coasts》2014,37(5):1107-1119

Sediment accretion was measured at four sites in varying stages of forest-to-marsh succession along a fresh-to-oligohaline gradient on the Waccamaw River and its tributary Turkey Creek (Coastal Plain watersheds, South Carolina) and the Savannah River (Piedmont watershed, South Carolina and Georgia). Sites included tidal freshwater forests, moderately salt-impacted forests at the freshwater–oligohaline transition, highly salt-impacted forests, and oligohaline marshes. Sediment accretion was measured by use of feldspar marker pads for 2.5 year; accessory information on wetland inundation, canopy litterfall, herbaceous production, and soil characteristics were also collected. Sediment accretion ranged from 4.5 mm year^?1 at moderately salt-impacted forest on the Savannah River to 19.1 mm year^?1 at its relict, highly salt-impacted forest downstream. Oligohaline marsh sediment accretion was 1.5–2.5 times greater than in tidal freshwater forests. Overall, there was no significant difference in accretion rate between rivers with contrasting sediment loads. Accretion was significantly higher in hollows than on hummocks in tidal freshwater forests. Organic sediment accretion was similar to autochthonous litter production at all sites, but inorganic sediment constituted the majority of accretion at both marshes and the Savannah River highly salt-impacted forest. A strong correlation between inorganic sediment accumulation and autochthonous litter production indicated a positive feedback between herbaceous plant production and allochthonous sediment deposition. The similarity in rates of sediment accretion and sea level rise in tidal freshwater forests indicates that these habitats may become permanently inundated if the rate of sea level rise increases.  相似文献   

Anomalous X-ray pulsars: persistent states with fallback disks     

Ü. Ertan  M. A. Alpar  M. H. Erkut  K. Y. Ekşi  Ş. Çalışkan 《Astrophysics and Space Science》2007,308(1-4):73-77

The anomalous X-ray pulsar 4U 0142+61 was recently detected in the mid infrared bands with the SPITZER Observatory (Wang, Chakrabarty and Kaplan: Nature 440, 772 (2006)). This observation is the first instance for a disk around an AXP. From a reanalysis of optical and infrared data, we show that the observations indicate that the disk is likely to be an active disk rather than a passive dust disk beyond the light cylinder, as proposed in the discovering paper. Furthermore, we show that the irradiated accretion disk model can also account for all the optical and infrared observations of the anomalous X-ray pulsars in the persistent state.  相似文献